1. Field of the Invention
The invention relates to apparatus used for assembling or disassembling members having mating threaded connections, such as pipe joints, threaded rods and bolts. More particularly, the invention relates to improved means to interconnect power-driven lead tong and back-up tongs, commonly used to make-up and break-out tubular goods used in earth boreholes, particulary in oil and gas wells. Additionally the invention relates to improved means to measure the torque applied to a threaded member by said tong combination.
2. Description of Prior Art
In virtually every industrial field there is at least some requirement for assembling and disassembling members having mating threaded connections such as, pipe, rods and bolts. Perhaps the best known requirement for making-up (or breaking-out) of such members exists in the earth boring industry, particularly that involving exploration for, and production of, oil and gas wells. In the oil and gas field, depending on the phase of operations being conducted, miles of drill pipe, hole casing or production tubing are necessarily assembled at the surface on a piece-by-piece basis. Similarly, each time it becomes necessary to remove pipe, casing or tubing from the borehole (for bit changes, pipe repair, pipe salvage or many other reasons), the string of pipe is progressively lifted from the hole, and disassembled at the surface on a piece-by-piece basis.
Because of the need to repetively make and break threaded member connections, various apparatus, generally referred to as tongs, more specifically lead tongs and back-up tongs, have been developed to facilitate that task.
As deeper wells are drilled the weight of the pipe string increases, as does the internal and external pressures the pipe must bear, thus greater demands are placed on the pipe, particularly on its threaded connections. In deeper wells pipe joints are often tightened to a high, extremely critical torque. Too low a torque can lead to leakage of drilling fluids or even the flammable fluids being produced. Too high a torque can damage the pipe joints and result in leakage or even separation of the pipe string in the hole. It is readily apparent that replacement or repair of damaged pipe, sometimes not discovered until the pipe is set in the borehole, is time consuming, dangerous and expensive.
It is readily apparent that during assembly and disassembly of a threaded connection there is no requirement for transverse (or lateral) (normal to the pipe axis) forces to be applied to said connection and, in fact such forces can have serious detrimental effects. Frictional forces due to lateral forces cause false torque reading and can cause premature thread galling. Said lateral forces can actually bend the pipe. Application of lateral forces during tightening can also cause the connection to tighten off center, which can result in loss of the connection's fluid seal.
While much of the prior art addresses other problems regarding use of tongs to assemble and disassemble threaded connections, the problem of lateral stresses has, hitherto, not been solved.
Kelley, U.S. Pat. No. 3,545,313, Dec. 8, 1970, discloses a combined lead tong ("grapple") and back-up tong. The lead tong and back-up tong are movable relative to each other along the axis of the pipe and the back-up tong is slidable toward and away from that axis. Relative turning movement of either the lead tong or the back-up tong is prevented by use of a single, interconnecting, rearwardly disposed shaft and sleeve arrangement. As is readily apparent this means of interconnection induces lateral forces on pipe joint during tightening or loosening. No means is disclosed for measuring the torque these tongs apply to the pipe joint.
Weiner, U.S. Pat. No. 4091,451, May 23, 1978, disclosed a method and apparatus for calculating the torque being applied to a pipe joint and for counting the number of turns of one member relative to the other. The invention discloses, in essence, a means for early detection of a "bad joint" being caused by lateral forces being applied during tightening, which causes "bending of one of the threaded members relative to the other, such as when rotating pipe sways, creates a false indication of reference torque . . . ". This invention detects some of the problems caused by the application of lateral forces during tightening or loosening, but does not prevent the lateral forces from occurring.
True, U.S. Pat. No. 4,125,040 discloses an apparatus for automatically stopping the application of torque to a pipe joint when a predetermined value has been achieved. The sensing means described is a strain gauge in a snubbing line. With reference to FIG. 1(a) herein, as is readily apparent, use of a snubbing line to restrain tong rotation about the pipe induces lateral stresses on the pipe joint during tightening or loosening.
Peveto, U.S. Pat. No. 4,170,908, Oct. 16, 1979, discloses a combined lead tong and back-up tong which is improved by the addition of an automatic indexing mechanism which aligns openings of the frame after make-up or break-out of a pipe joint. Also, disclosed is a pair of fasteners disposed on each side of the tong for purpose of suspending the back-up tong from the lead tong. Though not discussed, it appears that the fasteners are somewhat slidable in the direction of the pipe axis and toward and away from the pipe axis. No third slide, perpendicular to the slide allowing movement toward and away from the pipe axis, is provided. Without such slide lateral forces would be imposed on the pipe connection during tightening or loosening.
Eckel, U.S. Pat. No. 4,290,304, Sept. 22, 1981, discloses a back-up tong improved by the addition of an apparatus which automatically releases the back-up tong if the drill pipe begins to slip down into the borehole or the tongs are lifted prematurely. Disclosed therein is a "stinger" rearwardly disposed on the back-up tong frame which cooperates with a load cell and the lead tong to produce a torque measurement. With reference to FIG. 1 and FIG. 2, said stinger, either cooperating with a snubbing line or with a "reaction bar" attached to the lead tong, would induce lateral stresses on the pipe during tightening or loosening.
Kinzback, U.S. Pat. No. 4,346,629, Aug. 31, 1982, discloses a lead tong for use in making-up and breaking-out of joints of varying diameter. No specific means of restraining tong movement about the pipe or measuring torque is disclosed.
Mooney, U.S. Pat. No. 4,402,239 discloses a combined lead tong and back-up tong which rearwardly cooperate with a load cell to produce a torque measurement. The back-up tong is suspended from the lead tong by a plurality of vertical shafts which cooperate with elongated apertures through the back-up tong to allow some relative rotational movement between the tongs. The disclosed means of interconnecting the tongs does not prevent lateral forces on the pipe joint, in fact the rearwardly disposed rigid cooperation between the lead tong and back-up tong (through a load cell) induces lateral forces on the pipe joint during tightening or loosening.
Reinholdt, U.S. Pat. No. 4,492,134, Jan. 8, 1985, discloses a combined lead tong and back-up tong slidably mounted to a platform. The lead tong and back-up are interconnected by a plurality of hydraulic cylinders each of which is movable in any direction in a horizontal plane, rotatably or linearly, against "resilient" support elements. This invention does not prevent lateral forces from being applied to the pipe joint during tightening or loosening, but attempts to "compensate" for "traverse relative movements, which cannot be completely prevented".
Shewmake, U.S. Pat. No. 4,494,425, Jan. 22, 1985, discloses a combined spinning tong and back-up tong having a slidable interconnection between the tongs, along the pipe axis, to allow the distance between the tongs to shorten or lengthen as the pipe joint shortens during assembly or lengthens during disassembly. The disclosed means of interconnection, comprising no traverse slides, does not prevent lateral forces on the pipe joint during tightening or loosening.
None of these patents disclose the present invention. In each of these patents the means used to "hold" the tongs "in place", that is, restrain them from rotating about the pipe axis during tightening or loosening, whether by snubbing lines or by the interconnecting means disclosed, produce lateral forces on the pipe joint during said torquing process. Some of the patents disclose means of detecting the undesirable effect of lateral forces and some attempt to "compensate" for some of the undesirable effects of lateral forces, but none are directed to preventing those forces from arising.
When a lead tong is operated, a rotary element contained within the tong body grasps a first threaded member. A motor, usually hydraulic, contained within the lead tong body generates a "driving torque" which is applied to the rotary element to rotate it, and the first threaded member therein, in the desired direction. By operation of Newton's third law of physics (that is, in essence, "for every force there exists an equal and opposite force"), creation of the "driving torque" (which is applied to the threaded member) results in a "reaction torque", which is applied to the lead tong body in the opposite direction. This reaction torque must be counteracted, to secure the lead tong body from spinning about the pipe rather than driving the pipe itself.
Hitherto, prior art means for securing the lead tong body against rotation about the pipe were by use of a snubbing line, a "reaction bracket" which rigidly cooperates with back-up tongs, or multiple members which rigidly (or resiliently) cooperate with the back-up tongs. All of these conventional means produce linear, laterally directed and unpaired force vectors on the lead tong body. The lead tong body tends to move laterally in response to said linear force vectors, which said lateral movement is resisted by the pipe. FIG. 1(a) diagrams the lateral force vectors when a prior art snubbing line was used to secure the lead tong body against movement about the pipe. FIG. 1(b) diagrams the lateral force vectors when a prior art "reaction bracket", cooperating with the back-up tong, was used to secure the lead tong body against movement about the pipe. FIG. 1(c) diagrams the prior art lateral force vectors when a prior art multiple rigid interconnects, cooperating with the back-up tong, was used to secure the lead tong body against movement about the pipe.
With reference to prior art back-up tongs, a similar phenomena occurred. Means used hitherto to secure back-up tongs from rotating with the pipe resulted in a lateral force being applied to the second threaded member (lower pipe). The lateral force vector applied to the second threaded member (lower pipe) was equal in magnitude, but opposite in direction to the lateral force induced by the lead tong above. A combination of the lateral force imposed on the upper pipe by the lead tong and on the lower pipe by the back-up tongs produced a bending moment across the pipe joint being tightened or loosened. FIG. 2(a) diagrams the lateral force vectors, created by both the lead tong and the back-up tong, when prior art snubbing lines were used. FIG. 2(b) diagrams the lateral force vectors created by both the lead tong and the back-up tong when a prior art "reaction bracket" was used. FIG. 2(c) diagrams the lateral force vector created by both the lead tong and back-up tong, when prior art multiple rigid (or resilient) interconnects were used.
As is readily apparent, the application of lateral forces on a pipe joint during tightening or loosening can have serious undesirable effects. Extra, and uneven, friction forces (see FIG. 3) caused by such side-loading can cause premature galling of the threads. The extra frictional forces can cause a false measurement which results in the joint being inadequately tightened. Further, the joint could "freeze" with a lateral displacement of the threads, which causes poor fluid sealing, or, if the lateral displacement later resolves, the joint may then be inadequately tightened.
The invention disclosed herein represents a vast improvement over prior art.